DIY planaria death trap
I made this planaria trap by using a glass test vial and cut ballpoint pen tip. By inserting the ballpoint tip, it creates an inverted funnel with a small opening. I placed the trap with a food pellet bait on the substrate of my shrimp bowl, and almost immediately, I saw planaria, snails and shrimp migrate to and congregate at the entrance of the trap following the scent But only planaria could get through the small opening.
By next day, I saw quite a few planaria and detritus worms trapped, but surprisingly they seem to be all dead as they puffed up and not moving. So what is causing their demise: 1) Run out of oxygen as the opening is too small for circulation, 2) Planaria or detritus worms secrete toxin that poison themselves, or 3) They are not really dead, just too overfed to become incapacitated (unlikely as live planaria will quickly contract into a dot when I touch it)